Signficant loss of responsiveness when the directory tree is open

Description

Something is doing per-key logic relating to the directory tree.

Evidence for this is that the directory tree will collapse and reset per keystroke.

It also becomes annoyingly laggy to type while the directory tree is open. I can't type fast enough to outpace the key handling, but the lag is definitely high enough to exceed my perceptual threshold and be noticeable.